In a hugely controversial move, Facebook says users can once again post extremely violent videos -- including those of people being beheaded. It's a reversal of a five-month ban on such material.

The social media site began blocking members from posting extremely violent video clips back in May, but has now changed its policies.

It didn't make a major announcement of the reversal, but has confirmed the change after a user posted a video of a murder in Mexico. That clip remained online under revised rules that limit the circumstances in which violent videos can be shown.

Violent Video Viewing Could Cause Mental Trauma

The original ban came after protests by child protection and suicide prevention groups, who warned that viewing decapitation videos could result in people being traumatized.

They noted that although such material is available on other sites, Facebook's enormous popularity means the clips spread much more quickly and are often seen by people who weren't actively looking for violent content.

Those groups have now complained they weren't consulted before Facebook overturned the ban.

Facebook says allowing such clips helps users share their experiences and draw attention to terrorism and human rights abuses. It says the clips are being shown to condemn violent actions. (Source: bbc.co.uk)

Glorifying Violence Still Against Facebook Rules

According to Facebook, it will only remove videos if they appear to "glorify", or celebrate violence. It's not yet made clear exactly what the threshold will be -- for example, what will happen if the original poster condemns the content, but a large number of users post messages supporting the people carrying out the violence?

Facebook also says it will consider adding warnings so that people know an image or video is violent and disturbing and must actively click to see it. The site may also need to develop a system that blocks advertisements from automatically appearing next to such material. (Source: cnet.com)

Although murders can now be shown on the site, Facebook remains hesitant about nudity. The revised rules ban any images of a woman's "fully exposed breast." That wording appears to be designed to allow pictures of breastfeeding, which had previously been classed as a breach of standards.